The US House of Representatives passed a bill Saturday to give the postal service a US$25 billion infusion and halt changes Democrats said threatened the millions of mail-in ballots expected in November's presidential election.
The 257-to-150 vote, largely along party lines in the Democratic-led chamber, came as President Donald Trump called the legislation "another HOAX by the Democrats... without talking about the Universal Mail-In Ballot Scam that they are trying to pull off."
The bill is expected to die in the Republican-led Senate, with Senate Majority Leader Mitch McConnell calling it a "partisan stunt."
Americans are expected to vote by mail in massive numbers due to the coronavirus pandemic, but the President has opposed more funding for the cash-strapped US Postal Service (USPS), acknowledging the money would be used to help process ballots.
Mr Trump, who is trailing challenger Joe Biden in polls, also has repeatedly and baselessly linked mail-in voting to election fraud.
Postmaster General Louis DeJoy, a Republican fundraiser who Mr Trump appointed to head the postal service in May, has presided over the removal of mail collection boxes and processing equipment.
He has also overseen a cut in overtime pay for mail carriers, which a union leader told AFP has slowed delivery times nationwide, and reshuffled senior management.
The postal service has warned most states that it could not guarantee the on-time delivery of mail-in ballots.
USPS announced Tuesday it would hold off on operational changes until after the November 3 election.
But Democrats were not mollified and House Speaker Nancy Pelosi called lawmakers back from summer recess to consider the issue.
"Congress needs to take action now that will ensure our Postal Service can continue to deliver for America through this pandemic," House Majority Leader Steny Hoyer said.
"It's not a partisan bill," he said. "It's a bill for America's democracy."
Kevin McCarthy, the top House Republican, accused Democrats of "wasting precious time spreading Speaker Pelosi's mailbox myths," contending that the USPS was properly funded and could handle even 150 million ballots.
The Postal Service "it isn't being 'sabotaged,'" he said.
Mr DeJoy testified before Congress on Friday, denying allegations that recent changes at USPS were designed to slow down election mail, calling them "outrageous."
The US is home to the world's worst coronavirus outbreak and Americans are predicted to rely on vote-by-mail in record numbers, with an estimated three-quarters of voters able to do so this fall.